Evolutionary Operation (EVOP) is a methodology for continuous process improvement that employs design of experiments techniques incrementally to find the optimum conditions during regular operation of a full-scale production process. The underlying philosophy is that a process should be run in such a way as to not just produce a product, but also to generate information on how to improve that product.
To avoid unwanted changes in the process output, only small changes are made to the levels of the process variables. To determine the true effect of these changes, therefore, the runs need to be repeated a large number of times and the results averaged.
The National Institute of Standards and Technology (NIST) defines EVOP in this way:
An abbreviation for "evolutionary operation". An EVOP is a special type of on-line experiment with several distinguishing features:
1. The experimental material is production material intended to be delivered to customers.
2. In each experimental cycle, the standard production recipe is changed.
3. The experimental factor levels are less extreme than in conventional off-line experiments.
4. The experiment is run over a longer term with more material than in conventional off-line experiments.
Advantages of EVOP:
1. Because the changes are made while the production process is on-line, these runs would have been made anyway and thus result in very little additional cost.
2. The changes are made so as to cause very little disruption to the process, thus minimizing the amounts of unusable output.
3. It can be performed by the process operators themselves and doesn’t require resources in the form of skilled technicians or experts.
Disadvantages of EVOP:
1. Since production is ongoing, it is usually practical to vary only two or three factors at a time in any given phase of the investigation.
2. The results are realized at a slower pace than would have been possible with a large-scale DOE application by taking the process off-line.
The What, Why, When and How of EVOP from Quality Portal: - http://thequalityportal.com/articles/evop.htm